P0172

Diagnostic Chart (Part 1 Of 3):

Diagnostic Chart (Part 2 Of 3):

Diagnostic Chart (Part 3 Of 3):

Schematic:

CIRCUIT DESCRIPTION
In order to provide the best possible combination of driveability, fuel economy, and emissions control, the vehicle uses a closed loop air and fuel metering system. While in closed loop, the VCM monitors the oxygen sensor signal voltage. The VCM adjusts the fuel delivery, based on a signal voltage. The long and short term fuel values, which a scan tool can monitor, indicate a change made to the fuel delivery. Ideal fuel trim values are approximately 0 percent, or 128 counts. If the oxygen sensor signal indicates a lean condition, the VCM will add fuel. This results in fuel trim values above 0 percent. If the oxygen sensor detects a rich condition, the fuel trim values will read below 0 percent. This will indicate that the VCM is reducing the amount of fuel delivered. The VCM sets this DTC when it detects an excessively rich condition.

CONDITIONS FOR RUNNING THE DTC
^ No active HO2S DTCs
^ No active TP sensor DTCs
^ No active MAP sensor DTCs
^ No active EGR sensor DTCs
^ No active EVAP system DTCs
^ No active ECT sensor DTCs
^ No active MAF sensor DTCs
^ No active IAT sensor DTCs
^ No active VS sensor DTCs
^ No active misfire DTCs
^ The throttle position is less than 70 percent.
^ The engine speed is between 575 and 4,000 RPM.
^ The BARO more than 70 kPa.
^ The ECT is between 75 and 114°C (167-237°F).
^ The MAP is between 22 and 85 kPa.
^ The IAT is between -8 and 76°C (46-169°F).
^ The MAF is between 3 and 85 g/s.
^ The vehicle speed less than 85 MPH.

CONDITIONS FOR SETTING THE DTC
The average of the short term fuel trim values during a 120-second period indicates that a rich condition is present.

ACTION TAKEN WHEN THE DTC SETS

IMPORTANT: In order to complete a trip cycle for the fuel trim diagnostic, the fuel trim diagnostic test must enable and run according to the above enable criteria, and according to the conditions for setting the DTC. A trip is not considered complete until the VCM runs the fuel trim diagnostic.

When the current DTC initially sets, a software flag indicating an emissions-related fault sets for 3 trips. The flag will clear if the rich condition is no longer present. However, if the VCM detects the conditions for setting the current DTC during a trip while the flag is still set, the VCM turns on the Malfunction Indicator Lamp (MIL). The MIL remains on during all of the subsequent trips until the DTC has been cleared by service, or until the rich condition has not been detected and the conditions for checking the fuel trim have been met for 3 consecutive trips.

CONDITIONS FOR CLEARING THE MIL OR DTC
^ The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed.
^ A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle.
^ Use a scan tool in order to clear the DTCs.

DIAGNOSTIC AIDS
If using the diagnostic tables does not isolate the problem, monitor the long-term fuel trim (FT) and fuel trim cell while you operate the vehicle during various loads. This procedure may isolate the condition which caused the current DTC to set.

A condition that causes the DTC P0300, Engine Misfire Detected, can also set the current DTC. An extremely rich condition which sets the current DTC may cause a misfire at idle, and cause DTC P0300 to set. If you cannot determine the cause of the current DTC, and if DTC P0300 is also set, refer to DTC P0300 Engine Misfire Detected. P0300




Typical Fuel Trim Values
The fuel trim values table indicates the typical fuel adjustment values as displayed on a scan tool. Negative values, or a rich condition, indicates that the injector pulse width is being decreased in order to lean out the fuel mixture. Positive values, or a lean condition, indicates that the injector pulse width is being increased in order to richen the fuel mixture.

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
2. A more negative value indicates that the Vehicle Control Module (VCM) is leaning the fuel mixture. A more positive value indicates that the VCM is enriching the fuel mixture.
5. This step checks the fuel system for problems.